1. Field of the Invention
The invention relates to a steering column device.
2. Discussion of Background
In a vehicle steering system, an impact absorbing mechanism is provided, in which a steering column moves to the front of a vehicle in accordance with a movement of a driver to the front at the time of a vehicle collision so as to absorb an impact. Meanwhile, there is a position adjustable steering column device that enables a steering column to move in a tilt direction and a telescopic direction in order to perform tilt adjustment and telescopic adjustment of the position of a steering wheel.
In this type of position adjustable steering column device, a fastening mechanism is provided in order to fix the adjusted position of a steering column by fastening a side plate of a column bracket that is fixed to the steering column, by using a side plate of a fixed bracket that is fixed to a vehicle body. In Japanese Patent Application Publication No. 2009-29224 (JP 2009-29224 A), a plurality of tilt friction plates and telescopic friction plates are stacked. Each of the tilt friction plates has a fastening shaft insertion hole through which a fastening shaft is inserted, and is fixed to a column bracket, and each of the telescopic friction plates has a fastening shaft insertion hole through which the fastening shaft is inserted, and is fixed to a fixed bracket. When fastening is performed by a fastening mechanism, both of the friction plates are fastened and frictionally engaged with each other, thus increasing a binding force of both of the brackets.
In JP 2009-29224 A, when the numbers of the tilt friction plates and the telescopic friction plates, which are overlapped with each other, are the same, it is not possible to set a retaining force in a tilt direction and a retaining force in a telescopic direction independently from each other. When one tilt friction plate is provided on each of right and left sides, and three telescopic friction plates are provided on each of right and left sides, a retaining force in the tilt direction is small. Therefore, if a component of a load in the tilt direction at the time of a second collision is too large, slippage may occur in the tilt direction between both of the brackets. In such a case, since contact between the tilt friction plate and the telescopic friction plates is changed from a static friction state to a dynamic friction state, slippage may occur not only in the tilt direction but also in the telescopic direction. In other words, the retaining force at the time of a second collision may be reduced practically.